I've just started advanced Bio course and we're looking at ecosystems but I can't get my head around it.

The definition states that an ecosystem is a community interacting with the environment in an area.

Environment = the conditions in which a person, animal, or plant lives or operates.

So do different ecosystems have different environments? Like would a small pond IN a forest be two separate ecosystems? Or a river IN a rainforest – would the river and the rainforest be two different ecosystems?

2) And also I read that ecosystems can be as small as a pond in your garden but other ecosystems can be as big as a country-spanning forest. So what distinguishes how large an ecosystem is? And how do you distinguish between one ecosystem from another ecosystem?

Yep that's pretty much it. A lake within a forest is two different ecosystems and the same goes for a river running through rainforest.

The boundaries of an ecosystem are basically defined by different types of environments, so the size of ecosystem is governed by how large the area is where the environment is relatively similar.

Obviously you get different environmental conditions within ecosystems, e.g. the temperature and light within the water of a lake changes with depth, but on the whole the dominating factors are the same, e.g. the entire lake ecosystem is dominated by fresh water, the primary producers are phytoplankton and macroalgae and so on.

But the distinction between an environment and an ecosystem is the fact that when you refer to an ecosystem you're talking about the habitat, the organisms that live there AND how they interact and affect each other.

For example, in a forest ecosystem, the soil fertility influences what plants can grow there. At the same time that plants that grow there, drop their leaves which then decompose and over time alter the soil fertility. They're both affecting each other.

It took me a while to get it too, don't worry. It's really just all about interaction.

Eco system is a community of interacting organisms together with it's abiotic environment, through which energy flows and with in which nutrients cycle. An ecosystem is technically cover on a few square meters or may cover a portion of continent. An environment generally refers to the surroundings of various living residents.While an ecosystem is a community consisting of both living and non living things that works together.In general an ecosystem is by it's environment, and all organisms with in the ecosystem must work in tandem to create a successful living space.